Automatically operated clutches particularly for use in conjunction with vehicular automatic transmissions have been known for many years.
Of particular interest to the present invention is the type of clutch, well known to those skilled in the art, that utilizes prescribed amounts of fluid pressure to effect and maintain the clutch in a released condition and which is automatically applied by means of a resilient biasing means such as a spring when the fluid pressure is reduced below a prescribed value or is otherwise lost due to a failure of some kind in the fluid pressure system.
Such clutches when used in conjunction with vehicular automatic transmissions are operative to apply and release the clutch according to a program of signals, commonly speed signals, which correspondly disengage and engage the transmission from a drive member such as the vehicle's engine crank shaft to enable automatic shifting between change gear ratios provided by the transmission and for vehicle starting.
One type of automatic clutch uses fluid pressure to keep the clutch disengaged. A major disadvantage of such a type clutch is that should the fluid pressure drop below the value required to keep the clutch disengaged, the clutch might engage without warning to the operator which may cause undesirable movement of a stopped vehicle.
Hence, a need exists for a means to keep the clutch disengaged upon loss of fluid pressure when the vehicle is stopped or below a low vehicle speed to prevent unexpected movement of the vehicle.
In another type of automatic clutch, fluid pressure is used to keep the clutch engaged. A major disadvantage of such type clutch is that should the fluid pressure for one reason or another decrease below the value required to keep the clutch in the engaged condition, the clutch is automatically released which disengages the transmission from the engine drive member and results in vehicle free-wheeling without the ability to utilize engine compression as an aid in braking the vehicle.
In view of the above, a need also exists to provide a means to maintain the clutch in the engaged condition under circumstances of fluid pressure loss so as to at least maintain engagement between the transmission and the engine drive member for purposes of insuring at least some degree of control and the ability to utilize engine compression as an aid in braking the vehicle. The means for maintaining a clutch, of the type herein described, in an engaged condition is provided by including a latch member in the clutch control system which is operable to provide such function and which is distinguishable from the latch member disclosed in my copending application Ser. No. 713,054, filed Mar. 18, 1985.